JP2000323294A - Cold-cathode tube inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set an output current of a piezoelectric transformer at high accuracy and emit light in a stable operation range by amplifying or stepping down a signal, which is obtained by detecting the output voltage and current of a step-up transformer comprising a drive waveform generating circuit and a drive circuit by a current detecting circuit insulated direct-currently, by a detecting circuit, returning it to a drive waveform generating circuit, and holding the output current. SOLUTION: A drive waveform generating circuit 2 forms a drive control signal controlling the transmission frequency of a voltage control oscillator by luminance adjustment control information from a detection circuit 1, where voltage and current waveform information of a cold-cathode tube fluorescent lamp 7 is fed back, and a data input terminal 9. The cold-cathode tube fluorescent lamp 7 is lit by stepping up a piezoelectric transformer 4 driven by the drive circuit 3 through a current detection circuit 5. The piezoelectric transformer 4 automatically outputs a prescribed value of current by the repetition of the operation or the phases of the outputted voltage and current are approximately accorded with each other so as to be stabilized at a operation frequency of high electrical efficiency. In the case of breakage the fluorescent lamp, the drive waveform generating circuit 2 prevents the drive circuit 3 from operating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-cathode tube inverter for a backlight of a notebook computer or the like. More specifically, the present invention relates to an output current AC detection circuit and a structure for keeping the output current of a CCFL inverter constant.

[0002]

2. Description of the Related Art An inverter for turning on a backlight such as a cold cathode tube of a notebook personal computer is, for example, a 6-bit inverter.
Since a high voltage of about 00 V is required, an inverter of a type in which a power supply voltage is boosted by using a winding transformer has been used. However, in recent years, notebook computers have been rapidly reduced in size and weight, and as a result, winding transformers cannot be made thinner. Therefore, a cold-cathode tube inverter using a piezoelectric transformer capable of realizing a thin and highly efficient inverter has begun to attract attention.

Since a cold cathode tube inverter using a piezoelectric transformer is operated at a high frequency of 50 kHz to 200 kHz, the lighting operation of a cold cathode tube fluorescent lamp tends to be unstable. The unstable operation causes a problem that the life of the cold cathode fluorescent lamp is shortened. In addition, when the cold cathode comes off for some reason, there is a danger that the inverter circuit will operate abnormally and be ignited and destroyed.

For this purpose, a detection resistor circuit for detecting the cold cathode tube current of the cold cathode tube inverter is provided. A circuit of a conventional cold cathode tube inverter will be described. Fig. 2
It is a circuit block diagram of the conventional cold cathode tube inverter. The detection circuit 1 includes a comparator, and includes a drive waveform generation circuit 2
The brightness adjustment control is performed. The drive waveform generation circuit 2 outputs to the drive circuit 3 a drive control signal that has been subjected to amplitude modulation or pulse width modulation in accordance with the brightness adjustment control of the detection circuit 1.

A starting circuit 3 drives a winding type or piezoelectric type step-up transformer 4 in accordance with a drive control signal. The piezoelectric transformer 4 boosts the drive control signal and turns on the cold cathode fluorescent lamp 7. The current flowing through the cold-cathode tube fluorescent lamp 7 is converted into a voltage value by the detection resistor circuit 11 and is fed back to the detection circuit 1.

[0006]

However, since the detection resistor circuit 11 is grounded, the potential of one electrode of the cold cathode fluorescent lamp 7 is substantially at the ground level. As a result, the energy lost due to the stray capacitance between the light emitting area of the cold cathode fluorescent lamp 7 and the metal case of the backlight increases as the distance from the ground level electrode increases. Therefore, the life of the cold cathode fluorescent lamp 7 is liable to be deteriorated due to unevenness of position-dependent emission of light and consumption of electrodes due to abnormal discharge.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem. Specifically, the present invention eliminates the ground-type current value detection resistor circuit of a cold cathode fluorescent lamp,
By providing an AC detection circuit that does not perform DC coupling and eliminating the adverse effect that one electrode potential of the CCFL becomes almost the ground level, the stray capacitance between the CCFL and the metal case of the backlight is removed. The long-life of cold-cathode fluorescent lamps by uniform light emission and stable light emission that does not cause abnormal discharge by making the potential generated in the lamp symmetrical from the center position of the cold-cathode fluorescent lamp to both ends of the cold-cathode fluorescent lamp It is an object of the present invention to provide a cold cathode tube inverter circuit that can be implemented.

In the cold-cathode tube inverter constructed as described above, as can be seen from FIG.
Is composed of a coil and a capacitor, so that the cold-cathode fluorescent lamp 7 is not restricted to a DC level, and the potential of the cold-cathode fluorescent lamp 7 becomes DC-free. 7 is automatically stabilized so that the potential becomes symmetric from the center to both ends. As a result, potentials having the same absolute values with different signs are applied to the electrodes at both ends of the cold-cathode tube fluorescent lamp 7, and the ideal It can drive cold cathode fluorescent lamps.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of a cold cathode tube inverter according to the present invention. The detection circuit 1 includes a comparator and the like, and sends luminance adjustment control information to the drive waveform generation circuit 2. The drive waveform generation circuit 2 adjusts the brightness based on the voltage waveform applied to the cold cathode fluorescent lamp of the detection circuit 1 and the voltage effective value of the supplied current waveform, the current effective value, and the phase relationship information between the voltage waveform and the current waveform. Voltage control oscillator (VCO) according to control information and brightness adjustment control information from data input terminal 9
A drive control signal is generated by controlling the transmission frequency, amplitude voltage modulation, or pulse width modulation (PWM), and outputs it to the drive circuit 3.

The starting circuit 3 drives a winding type or piezoelectric type step-up transformer 4 in accordance with a drive control signal. The piezoelectric transformer 4 boosts the drive control signal and turns on the cold cathode fluorescent lamp 7 through the AC detection circuit 5. The voltage applied to the cold-cathode tube fluorescent lamp 7 and the flowing current are
And is fed back to the detection circuit 1 in the form of an AC waveform. The detection circuit 1 receives the voltage waveform and the current waveform detected by the AC detection circuit 5, converts the current waveform into a voltage waveform, amplifies the voltage waveform, and sends it to the drive waveform generation circuit 2. By repeating the above feedback loop, the output voltage and output current of the piezoelectric transformer 4 automatically become desired current values. further,
By making the phases of the output voltage value and the output current value substantially coincide with each other, the operating frequency of the CCFL inverter is automatically stabilized at a frequency with good power efficiency, and the CCFL 7 is turned on in an optimal state. Can be.

When the cold cathode fluorescent lamp 7 is damaged and the output of the piezoelectric transformer 4 is released, the AC detection circuit 5
Cannot detect current. After detecting the detection for a certain period of time, the drive waveform generation circuit 2 restricts the operation of the drive circuit 3 when detecting the abnormality of the detection circuit 1. Further, the drive waveform generating circuit 2 may determine whether the abnormal output voltage is output due to the disappearance of the output load of the piezoelectric transformer 4 or that the output load of the piezoelectric transformer 4 is reduced due to the short circuit and the excessive current is generated. Is output from the information output terminal 8 to the outside.

By providing a system for recording this information, dangerous restart can be prevented and quick repair can be performed. The data input terminal 9 of the drive waveform generation circuit 2
This terminal receives information such as luminance control, ON / OFF control, minimum luminance value setting, maximum luminance value setting, and the like. FIG.
It is a schematic circuit diagram of an alternating current detection circuit and a detection circuit of the present invention.
The AC detection circuit 5 includes a current detection coil 1 of the output wiring 10.
2 and a capacitor 13 for voltage detection. Coil 12
Are connected to the current amplification circuit 14 of the detection circuit 1. By providing a capacitor on the input side of the current amplifying circuit 14, a resonance circuit is configured with the coil 12, and the detection sensitivity of the output wiring 10 to the alternating current is improved. Capacitor 13
Are connected to the current amplification circuit 15 of the detection circuit 1. Since the voltage of the output wiring 10 reaches several hundreds to several kilovolts, a voltage dividing circuit having a high resistance is provided on the input side of the voltage amplifying circuit 15. A protection circuit such as a diode is not shown. Current amplification circuit 14 and voltage amplification circuit 15
Is output to the drive waveform generation circuit 2.

FIG. 4 is a structural diagram of Embodiment I of the transformer of the AC detection circuit of the present invention. The output wiring 10 formed on the surface of the circuit board is meandering and forms a primary coil of a transformer which is almost one loop. The secondary coil 12 of the transformer is a flat spiral coil. Example
In I, a flat spiral coil is formed on the front surface and the back surface of the circuit board, and is connected by the through hole 16 to obtain an inductance value. When it is necessary to enhance the magnetic coupling in order to enhance the detection sensitivity of the coil of the output wiring 10 and the coil 12 constituting the transformer, board holes 17 and 18 are provided on the circuit board at the center of each coil to provide two holes. Ferrite 1
At 9, the magnetic coupling is performed.

FIG. 5 is a structural diagram of Embodiment 2 of the transformer of the AC detection circuit according to the present invention. The output wiring 10 forms a primary coil of a one-loop transformer using a lead terminal 21 of a connector 6 connected to a lead wire to the cold-cathode tube fluorescent lamp 7 connected via a connection unit 20. . The secondary coil 12 of the transformer is formed by a flat spiral coil on the back surface of the circuit board. If the circuit board has three or more layers, the inductance value can be increased by forming a flat spiral coil also in the inner layer. To further enhance the magnetic coupling, a board hole 22 is provided in the circuit board at the center of the coil, and a ferrite 23 is arranged at the center.

The structural diagrams of the embodiment I and the embodiment II are such that when the output wiring 10 forms a planar spiral coil, there is no through hole. This is to prevent the power efficiency of the cold-cathode tube inverter from decreasing due to the increase in the output impedance. Example II
The planar dimension of the transformer can be made smaller than in Embodiment I. Further, in Example I and Example II, since a coil having high dimensional accuracy is formed by the wiring pattern on the circuit board, variation in the performance of the transformer can be reduced.

[0016]

As described above, according to the present invention, the AC detection circuit for detecting the output of the piezoelectric transformer is constituted by an AC-coupling coil, particularly a high-precision transformer and a capacitor formed of a circuit board, and amplified by the detection circuit. Then, the output of the drive circuit was controlled by feeding back to the drive waveform generation circuit and performing frequency modulation control and pulse width modulation control based on the phase information of the voltage value applied to the CCFL and the current value flowing therethrough. Thus, the output current of the piezoelectric transformer can be maintained at a highly accurate set value, so that there is an effect that a cold-cathode tube inverter circuit that can emit a cold-cathode tube fluorescent lamp in a stable operation region can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a cold cathode tube inverter according to the present invention.

FIG. 2 is a circuit block diagram of a conventional cold-cathode tube inverter.

FIG. 3 is a schematic circuit diagram of an AC detection circuit and a detection circuit according to the present invention.

FIG. 4 is an embodiment I of a transformer of an AC detection circuit according to the present invention;
FIG.

FIG. 5 is an embodiment of a transformer of an AC detection circuit according to the present invention.
FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detection circuit 2 Drive waveform generation circuit 3 Drive circuit 4 Piezoelectric transformer 5 AC detection circuit 6 Connector 7 Cold cathode fluorescent lamp

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[Procedure amendment]

[Submission date] May 21, 1999 (1999.5.2
1)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 2

[Correction method] Change

[Correction contents]

FIG. 2

Claims (4)

[Claims] 1. An illumination cold-cathode tube inverter comprising a driving waveform generation circuit, a driving circuit, and a step-up transformer, wherein a direct current insulation for detecting an output voltage and an output current of the step-up transformer connected to the cold-cathode tube fluorescent lamp is provided. The detected AC detection circuit, a detection circuit for amplifying or stepping down the signal detected by the AC detection circuit, and feeds back the information of the output current and the output voltage output from the detection circuit to the drive waveform generation circuit. A cold-cathode tube inverter having a circuit configuration for holding the output current. 2. A cold cathode tube inverter for lighting,
2. The cold-cathode tube inverter according to claim 1, wherein a transformer for detecting an output current and a capacitor for detecting an output voltage are provided between the output of the transformer and the cold-cathode fluorescent tube. 3. The detection transformer according to claim 2, wherein the detection transformer is configured by pattern wiring on a circuit board.
A cold cathode tube inverter as described. 4. The cold-cathode tube inverter according to claim 2, wherein a part of a coil wiring of the detection transformer is formed by a lead terminal of a connection connector of the cold-cathode tube fluorescent lamp.